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Monday, February 8, 2010

Useful Command line little tricks (part 1)

Before I started using Linux, I never really understood why people would use the command line, much less why they would consider it such a powerful tool. I always thought I could do just as much from the GUI, and even quicker. Sadly, I have come to an understanding quite late, but as they say, "better late than never"!

Ultimately, if you use the GUI, you learn to use that interface, but you are missing on how the OS actually works. Believe me, when you start getting an understanding on how the system works and what it does, when you start to get where to look when something fails or what to change in order to fix it, that's when you experience a great feeling of empowerment. On top of that, the GUI is great for certain activities, but it is very limiting when it comes to others.

Obviously, I am sure you have read very similar statements before, and none have convinced you to actually learn to use the command line. Guess what? I am not going to try to. All I want to do is explain some of the basics. If after reading this you feel you are the kind who might enjoy understanding how the computer does what it does, then you might actually want to jump into the cold waters after me. Otherwise, I hope this was not too boring!

First off, I want to provide some background about the shell as it stands in Linux today. I also want to share some interesting commands I use regularly, which might help you as well. Let's start with some basic concepts:

WHAT IS BASH?

BASH is a command interpreter that is widely extended in the Linux world. It is the GNU reinterpretation of the Bourne Shell (an important early UNIX shell created by Stephen Bourne). In fact, Bash is an acronym, a pun on the name Bourne Shell and the term "born again", thus Born Again SHell.

THE LINUX FOLDER STRUCTURE

If you run this simple command,

ls /

you should get your basic folder structure under the root directory, looking something like this (displayed as a list here for formatting reasons):

Let's see what some of those folders are used for in Linux. Understanding the basic folder structure will help you in seeing the big picture!

BOOT folder

Contains the Kernel, some drivers that may be required at boot time, and the boot loader. In the current version of Ubuntu, that turns out to be GRUB2. For example, if you wanted to take a look at the GRUB2 script that controls the boot of your system, you can do so by running the following command (note that this file is not meant to be manually edited):

less /boot/grub/grub.cfg

DEV folder

Contains a list of all the devices (actually, device nodes) recognised by the kernel. For example, your hard drive is mounted under one of these nodes, most probably SDA1. For a list of all device nodes, you can run the following command:

ls /dev

ETC folder

Contains system wide variables, such as passwords, information about file systems, and even your repository sources. You may have actually edited those sources manually already, but if you have not, you could do so by running the following command:

sudo gedit /etc/apt/sources.list

You could obviously run it with any other visual text editor, or even with nano or vi, whatever your preference.

HOME folder

Here's where ordinary users folders are stored, and for the most part, it will be the only location you have rights to modify in a properly configured Linux system. This is actually one of the features showing the strength of Linux security. As opposed to Windows, where any user can go ahead and save or modify files under C:\windows\system32, for example, nobody can do such changes in Linux out of the box.

MEDIA folder

Here's where modern Linux systems mount removable drives. USB external drives, CD and DVD devices... They all are listed under this folder.

OPT folder

Optional software is stored in here. As an example, I have Adobe AIR and TweetDeck stored under this folder.

USR folder

Contains general applications used by standard users. It usually is a very large folder, as it contains hundreds of applications. Some interesting folders under the USR one include the BIN folder, which contains the applications themselves and the LIB folder, which holds documentation for those applications.

USR/SHARE folder

This folder deserves a bit more attention due to the useful information it contains. It basically holds shared data used by applications under /usr/bin. For example, you can find your system icon themes under /usr/share/icons/themes.

VAR folder

The information that is likely to change is stored under this folder. For example, we can find logs, which are stored under the log folder. In order to take a quick glance at the latest changes in your system log, you can try the following command:

less /var/log/syslog

You can also check boot logs to check if you had issues when starting up your machine:

less /var/log/boot

TO BE CONTINUED...

Let's stop here, as there is a lot of information already for you to digest!. I very much encourage you to investigate your system folder structure. Understanding its logic will get you closer to understanding your system, which is already quite a step forward.

In the next installment of these series, I will cover some commands that I often use. I hope you find them just as useful!